The purposes of the project are (1) to explore the role the nursery school teacher in sex role differentiation; (2) to trace the development of aggressive, dependent, and cooperative behaviors in preschoolers; (3) to examine these behaviors as they relate to sex, age, intelligence, and socioeconomic status; (4) to see whether nursery school teachers reinforce these behaviors differentially based on the sex of the child; and (5) to see how sex role identification changes during the nursery school years. The above problems are approached through an incomplete cohort-sequential design. Three-, four-, and five-year-olds in nursery school are being followed throughout their nursery school careers. Children are given pre- and posttests each year on various measures of intelligence and sex role identification. Children and teachers are also observed every two weeks in their classrooms. Concurrent relations between data from these two data sources as well as longitudinal relations will be examined.